A fluidized bed apparatus is used for making medicaments. The medicament starts as a bead which is coated with conventional additional materials within a mixing cylinder. By controlling the particle size distribution and the amount and nature of the particles, the final product can be provided with sustained release properties. The final product typically weighs two to six times the initial wieght of the bead.
Conventional fluidized bed apparatuses employ mechanical stirring devices, such as rotating blades, on the bottom of the mixing cylinder for maintaining the beads in continuous rotational movement. Adhesive and powder are delivered by spray or other means into the mixing cylinder. The beads become coated with the adhesive and grow in size by picking up the powder which will stick to the adhesive.
The use of mechanical stirring devices, such as blades, is disadvantageous because the blade breaks up some of the beads, is difficult to clean (which can result in cross contamination between product batches and down time for cleaning), the effectiveness of the blade is impaired when particles, adhesive, and powder build up thereon, and there is a risk of explosion from sparks.
Alterman U.S. Pat. No. 3,908,045 does not use mechanical stirrers. It employs a fluidizing gas that enters the vessel from beneath the mixing cylinder. In addition, a small amount of tangential air is supplied through a series of nine tubing jets that are equally spaced about the inner perimeter at the support screen level. The "function of the air jets is to help provide uniform particle coating by preventing any stagnant bed areas from forming at the wall" (column 7, lines 10-13).
Prior art patents with mechanical stirring devices include Funakoshi et al U.S. Pat. No. 3,671,296. It discloses an apparatus in which granules are charged into a receptacle and the dish is rotated by a motor, causing circulation of the granules about the axis of rotation. Centrifugal force pushes the granules outwardly and upwardly, and coating materials are applied to the circulating granules. Dry air is then blown into the receptacle and through the coated granules. Dry air is fed through an air inlet provided on the bottom of the receptacle and through vent holes and a ventilation gap.
Irikura et al U.S. Pat. No. 3,711,319 discloses a process for coating particles in which hot air is blown in below a horizontally rotating disk and is guided upwardly between a coating tower and the periphery of the disk. Particles of powder to be coated are supplied into the tower above the disk, and coating materials are sprayed into a flowing fluidized bed of the particles developed by the upward flow of air above the disk and the centrifugal force of the disk. This is also disadvantageous by requiring a mechanical stirring device.